18.60. Set Up: Solve: (a) so (b) so 18.61. Set Up: The stored energy is Solve: (a) (b) Reflect: There are three equivalent expressions for the stored energy and we can choose the one most appropriate to the information we are given. 18.62. Set Up: The energy stored in a capacitor is The charge of an electron is Solve: (a) The number of electrons with this magnitude of charge is (b) To double the stored energy, halve the capacitance. To do this, either double the plate separation or halve the plate area. 18.63. Set Up: The two capacitors are in series. For capacitors in series the voltages add and the charges are the same. Solve: (a) so (b) for each capacitor. (c) (d) We know C and Q for each capacitor so rewrite U in terms of these quantities. 150 nF: 120 nF: Note that the total stored energy calculated in part (c). 150 nF: 120 nF: Note that these two voltages sum to 36 V, the voltage applied across the network. Reflect:

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